The most common complaint about a new custom shower is not the tile. It is that the rain head and the hand shower will not run properly at the same time.
Shower systems are sold by the outlet: rain head, hand shower, body sprays, a tub filler on the same valve. Each outlet has a flow rate, and they add up. Whether your house can deliver that total is a plumbing question, and it has to be answered before the custom shower is roughed in, not after.
Add up the outlets
A 10-inch rain head is typically 1.8 to 2.5 gallons a minute. A hand shower is similar. Four body sprays can be 1 gallon a minute each or more. Run a rain head, a hand shower and four sprays together and you are asking for 8 to 10 gallons a minute through one valve, and more if the system is a high-flow model. Most residential fixtures are designed around a house that delivers 5 to 7 gallons a minute at the shower.
What limits the flow
- The service. Many Lower Mainland houses have a 3/4-inch water service; older ones have 5/8-inch or 1/2-inch. The service is the ceiling for the whole house.
- The branch. A 1/2-inch branch to the bathroom will not carry 10 gallons a minute at usable pressure. A high-flow shower wants a 3/4-inch branch to the valve.
- The valve. A standard half-inch thermostatic valve passes less than a 3/4-inch high-flow valve. The valve and the branch must match.
- Pressure. Static pressure of 60 psi means little if running pressure collapses to 30 when two outlets open. We measure both.
- Hot water. A 10-gallon-a-minute shower empties a 50-gallon tank in a few minutes. The water heater sets the length of the shower.
How we check before we commit
We measure static and running pressure at an outside tap, confirm the service size at the meter, trace the branch that will feed the bathroom, and read the flow rates off the fixture specifications rather than the brochure. Then we size the branch, pick a valve that matches, and size the hot water. If the service is the limit, the honest answers are a booster pump, a service upgrade, or a system with fewer simultaneous outlets. We would rather say that at the design stage than after the tile.
Hot water options that keep up
For a bathroom with a large shower and a soaker tub, a condensing boiler with an indirect tank gives the recovery rate a tank cannot. A correctly sized tankless unit works if the gas supply and venting allow it. A recirculation loop means hot water arrives at the rain head in seconds rather than a minute, which matters more in a long shower than anywhere else in the house.
The rest of the rough-in
Flow is one item on a longer list: valve depth, drain position, blocking, access, steam. Our rough-in checklist walks through all of it, and the luxury bathroom plumbing page covers how we work with designers and builders. If the project includes a steam shower, the generator and its drain join the same conversation.
We are brought in when the fixture package is the point. See high-end plumbing in the Lower Mainland for the full picture.
Related guides
- Our Philosophy: Do It Right, Do It Once
- Resource: Understanding BC Plumbing Code
- Pro-Press Tech: No Flames, Just Permanent Seals
- The Seastack Standard: Why Quality is Invisible
